An Internet Protocol (IP) network routes an IP packet based on an IP address in the packet. A router in the IP network typically enters an internal routing table with the IP address to yield a prioritized list of links to other routers or nodes. The router then transfers the packet over the highest priority link in the list. In some cases, a first router will instruct a second router to lower its route priority to the first router for a given IP address. When the second router enters its internal routing table with the given IP address, it will probably not select the lowered priority link to the first router.
If the IP network uses a Transmission Control Protocol (TCP), then the routers send acknowledgements back along the packet path if the IP packet correctly reaches its TCP destination. If the IP network uses a User Datagram Protocol (UDP), no such acknowledgements are sent back. The IP network may also transfer packets over different routes. This can be accomplished by establishing two IP tunnels that use different IP routing, so they traverse physically separate routes.